The inventor of the present invention has proposed a field effect transistor in which a liquid electrolyte has been used as a gate, and a hydrogen terminated surface of a diamond has served as a channel (refer to the following Patent Documents 1 and 2).
It is known that urea is hydrolyzed by the catalysis of urease (enzyme), ammonia is generated, and the pH is increased. In a silicon based ion-sensitive field effect transistor (ISFET), urease (enzyme) is immobilized on a silicon nitride serving as a protective-sensitive film and, thereby, a change in pH is detected. In this case, the detection accuracy depends on the immobilization density and the immobilization strength. Although there is a method in which urease (enzyme) and the ISFET are separated, in this case, a problem occurs in that the detection sensitivity is reduced.
[Patent Document 1]
Japanese Patent No. 3313696 (pages 2 to 4, FIG. 1)
[Patent Document 2]
Japanese Patent No. 3390756 (pages 2 to 4, FIG. 1)